Koch Institute Members use vertebrate model organisms as a key tool to study the role of known or putative cancer genes in development and tumorigenicity; investigate the mechanisms of tumor initiation, progression and metastasis; evaluate the role of stroma and immune responses in tumorigenesis; and assess the efficacy of drugs, nanomaterials and devices in therapeutic and diagnostic applications. Thus, it is essential that Center Members are able to correctly diagnose developmental and tumor phenotypes, evaluate the underlying molecular events, and accurately and quantitatively assess drug or vaccine delivery and therapeutic response. The Koch Institute Histology Core is a Shared Resource that provides state-of-the-art histological services to support these studies. This includes assistance and/or training in tissue sectioning, slide preparation and analysis, and access to the consultative services of an internationally recognized Veterinary Pathologist, Dr. Roderick Bronson for diagnosis of tumor and developmental phenotypes. In the current period, the capabilities of this Core have been expanded and enhanced. This includes moving into a larger, custom-designed space in the new Koch Institute building, an increase in the staff and the acquisition of new instrumentation including the addition of automated immunohistochemistry and special staining capabilities. Notably, in the same period, usage of the Histology Core by Center Members increased from 53% to 67%, and included investigators from all four Programs. Thus, this Shared Resource is essential to the success of the Koch Institute mission. In the upcoming period, the Histology Core will continue to offer a wide range of state-of-the-art histological services to support the research programs of Center Members. In spite of the significant expansion of services, and the resulting increased costs of running this Core, the requested CCSG budget for Year 44 is essentially the same as the requested and recommended budget in Year 39.